1. Field of the Invention
The present invention relates to an apparatus and method for network communication, and more particularly to a communications network arranged with clusters of stations, each cluster having a head, with each of the stations affiliating, when possible, with two or more cluster heads.
2. Related Art
Communications networks can be formed by arranging a plurality of mobile communications stations into a hierarchical configuration including groups (or xe2x80x9cclustersxe2x80x9d), with each group having a group or cluster head (or xe2x80x9ccluster gatewayxe2x80x9d). Many conventional networks confine their configurations by predetermining or preselecting access points, even though the networks may allow a member station to switch affiliation from one access point to another. For example, in some mobile-radio networks, there can be a hand-off of a mobile unit from one base station to another, the hand-off being initiated by the base station. Oftentimes, these types of gateway stations are stationary or immobile, further limiting the flexibility of the network.
An example of a flexible mobile communications network is disclosed in U.S. Pat. No. 5,850,592, issued to S. Ramanathan on Dec. 13, 1998, and assigned to the same assignee. The U.S. Pat. No. 5,850,592 discloses a method for a plurality of mobile stations to automatically organize themselves into a hierarchical network, in which some of the stations operate as message gateways for a cluster of mobile stations.
In the arrangement of the U.S. Pat. No. 5,850,592, a plurality of mobile stations are employed, with each station being able to operate in at least two basic modes. In a first mode, the mobile station serves as a message gateway (e.g., a xe2x80x9ccluster headxe2x80x9d or xe2x80x9cnetwork access pointxe2x80x9d) for a cluster of other member stations (e.g., xe2x80x9cnon-gatewayxe2x80x9d stations). The second mode allows the mobile station to operate as a non-gateway (or xe2x80x9ccluster memberxe2x80x9d) station. Each mobile station determines which out of the two modes to operate in.
The mobile stations disclosed in the U.S. Pat. No. 5,850,592 are capable of operating at two different power levels. When operating as a cluster head, the mobile station transmits at a relatively high power level. The cluster head transmits at the relatively high power level to communicate with other cluster head stations and to typically provide longer distance network links. Although the cluster head communicates at a higher power level with other cluster heads, the cluster head can still communicate with its cluster members using a relatively lower power level. A cluster head can also periodically broadcast a so-called beacon message to establish the station""s presence and its availability to operate as a cluster head. The beacon message may contain address or node-identifying information, affiliation information, and communication protocol information, for example.
Cluster head stations communicate with each other to form a network backbone. Cluster member stations affiliate with only one cluster head at a time. A possible network arrangement is shown in FIG. 8. Each cluster member (2axe2x80x2-2dxe2x80x2) includes the ability to affiliate with a cluster head (e.g., 1axe2x80x2-1cxe2x80x2), and if a cluster head is not available, to commence operation as such.
Each cluster head station also is equipped to identify whether any other cluster heads are within affiliation range, and if so, to initiate a procedure to terminate operation as a cluster head, if such termination will not reduce connectivity of a network backbone excessively. Before terminating operation as a cluster head, the cluster head can broadcast a termination request and wait for a predetermined time to see if the request is accepted by all members. In known systems as exemplified by the U.S. Pat. No. 5,850,592, each cluster member has only a single cluster head, and all communications traffic goes through that cluster head. If the single cluster head is lost unexpectedly, for example in a military operation or in an emergency situation (e.g., a natural disaster), the cluster member is temporarily cut off from the network. As a result, the cluster member must start a cluster affiliation protocol to reestablish a relationship with an available cluster head. If the cluster member cannot establish a link with a cluster head, it will then promote itself to be a cluster head, and seek affiliation with other cluster heads. These steps consume valuable time. During this xe2x80x9cdown time,xe2x80x9d the cluster member is temporarily cut off from the network. Severing communications in an emergency or in a military operation can produce catastrophic results.
These types of problems are not adequately addressed in the art. Thus, there is a need for a flexible communications station in a communications network to simultaneously affiliate with multiple clusters, instead of just a single cluster at one time. There is another need to provide an adaptive, wireless mobile communications station with the ability to automatically organize with other similar mobile stations into a network, the stations each being able to gain affiliation with multiple groups.
The present invention relates generally to a station capable of belonging to multiple clusters in an ad hoc wireless network.
According to the invention, a communications system for communication among plural stations in a network is provided in which stations are arranged in clusters of communication member stations each communicating with each other and one of the member stations is a head station of the cluster. Each cluster head station communicates with other cluster head stations.
According to one aspect of the invention, a method is provided including (i) determining a communication state between a station and one or more cluster head stations; and (ii) assigning the station to the one or more clusters when a prescribed communication state has been determined between the station and the cluster head stations, wherein the station is set to be in independent communication with the one or more cluster head stations having the prescribed communication state with the station.
According to another aspect, the station is assigned to plural clusters when the prescribed communication state with plural cluster head stations has been determined and is in independent communication with each of the plural cluster head stations.
According to still another aspect, the station is set to be in concurrent communication with the plural cluster head stations with which the station has the prescribed communication state.
According to yet another aspect of the present invention, the assignment of the station to each of the plural clusters is preformed asynchronously. Furthermore, the prescribed communication state is based on at least one of an evaluation of a received signal strength from each of the cluster head stations, successful receipt of a predetermined number of messages from each of the cluster head stations, a ranking according to administrative function, and the numbers of stations within a cluster.
According to yet another aspect of the invention, the station is assigned to be a cluster head when the prescribed communication state has not been attained with any of the cluster head stations.
According to yet another aspect of the invention, data messages are sent via one of the cluster head stations of the clusters to which the station is currently assigned. Also, data messages are received through one of the cluster head stations to which the station is currently assigned.
According to yet another aspect of the invention, an assignment of a station to a cluster can be switched, but assignment of the station to at least one cluster is maintained.
According to still another aspect of the invention, a status of the assignment of the station to other stations is periodically relayed. Furthermore, the assignment of the station is maintained with the plural clusters for a randomly selected time.
In one embodiment, the station according to the invention is a mobile station, and the communications network is a mobile communications network.
In another embodiment, a method of operating a communications station for communicating among a plurality of communications stations in a communications network, is provided. Each station is able to receive and transmit signals, the stations being arranged into cluster groups each having at least one station. Each cluster group includes at least one station designated as a cluster head. The method includes (i) recognizing a plurality of cluster heads for potential affiliation with the station; (ii) deciding a subset of the recognized cluster heads for the station to affiliate with; and (iii) allowing the station to concurrently affiliate with at least two cluster heads of the subset.
In still another embodiment, in a mobile communications network employing a plurality of mobile stations, a method of operating a mobile station so as to automatically configure the plurality of stations into a network for relaying messages from station to station is provided. The method includes (i) determining possible network access points to the mobile communications network; (ii) attempting to establish a simultaneous communication affiliation with at least two network access points, and establishing simultaneous communication affiliation with the at least two access points if possible, wherein a communication affiliation with each of the at least two access points is independent from one another; (iii) and allowing the mobile station to change network access points.
Another embodiment relates to a mobile communications station for communicating among a plurality of mobile stations in a network in which stations are arranged in clusters of communication member stations. Each of the member stations communicate with each other and one of the member stations is a head station of the cluster, the cluster head stations communicate with other cluster head stations. The mobile communications station includes a transceiver. The mobile station includes a processor which: (i) determines a communication state between the mobile station and one or more cluster head stations; (ii) assigns the mobile station to the one or more clusters when a prescribed communication state has been determined between the station and the cluster head station; and (iii) sets the station to be in independent communication with the one or more cluster head stations having the prescribed communication state with the station.
Still another embodiment relates to computer executable code stored on a computer readable medium. The code is for operating a communications station so as to communicate with a plurality of mobile stations in a network in which stations are arranged in clusters of communication member stations and one of the member stations is a head station of the cluster. The cluster head stations communicate with other cluster head stations. The computer executable code includes: (i) computer executable code to determine a communication state between a station and one or more cluster head stations; (ii) computer executable code to assign the station to the one or more clusters when a prescribed communication state has been determined between the station and the cluster head station; and (iii) computer executable code to set the station to be in independent communication with the one or more cluster head stations having the prescribed communication state with the station.
Yet another embodiment relates to a network communications apparatus. The apparatus includes a memory, processor, and transmitter. The memory stores network topology information. The processor (i) facilitates communication with multiple communication gateways in the network, and (ii) determines a lowest-cost routing path for message transmission through the network based on the network topology information. The transmitter transmits messages to communication gateways.
Still another embodiment relates to a network communications apparatus. The apparatus includes means for storing, means for facilitating, means for determining, and means for transmitting. The storage means stores network topology information. The facilitating means facilitates communication with multiple communication gateways in a network. The determining means determines a routing path for message transmission through the network based on the network topology information. The transmitting means transmits messages to communication gateways.
These and other objects, features and advantages will be apparent from the following description of the preferred embodiments of the present invention.